Prescaler Spurs intermodulation in pll

[hosein_rabiee_g]

Hi.
I make a pll synthesizer and used hmc363 for rf prescaler.
the synthesizer work at 7.6GHz and the prescaler output is 950MHz.
But spurs with -60dBc Power level exist at the output in 9.5GHz and 5.7GHz.
I think these are IMD of 7.6GHz and 2nd Harmonic of 950MHz but the datasheet says that these mudt be below -100dBc.
Any body can help me?

 

[FvM]

but the datasheet says that these mudt be below -100dBc.

Which datasheet specification do you refer to?

You would primarly look for prescaler reverse leakage and possible intermodulation effects in the VCO. Generally speaking you'll want to improve the VCO to prescaler isolation and check for unwanted pathes through that the prescaler output signal can enter the VCO circuit.

 

[tony_lth]

obviously 9.5G is 10th harm. of 950M, and 5.7G is 6th.

 

[hosein_rabiee_g]

Ok.But prescaler doesn't produce the even harmonics of output.

 

[FvM]

Ok.But prescaler doesn't produce the even harmonics of output.

How do you know?

Perhaps 3th and 5th harmonic of 2*950 MHz, a signal inside the prescaler, sounds more plausible. In any case, reverse leakage or insufficient power supply decoupling can easily explain the problem.